MIC Flashcards
What percentage of childhood deaths (kids under 5 are caused by diarrhoea)?
about 11%
Describe the two ways in which diarrhoea kills?
Immediate: due to a fluid and electrolyte imbalance
Delayed: mainly due to malnutrition
What is the association between diarrhoea and malnutrition?
It causes increased energy loss. This is due to diarrhoea, vomiting and increased metabolic needs.
Reduced energy intake. When the gut is inflamed food is malabsorbed.
An additional problem is that when kids have diarrhoea and malnutrition mothers (mainly in the 3rd world) think that it has something to do with the milk/food that the kids are eating and withhold it, this is very dangerous
How much fluid goes through the gut and how much is reabsorbed in 24 hours?
10L in
9.9L reabsorbed
About 100ml comes out in faeces
In L how much fluid is secreted by each of the regions of the GIT?
Mouth 2L (eg from food and drink) Salivary glands 1.5L Stomach 2.5L Liver (bile) 0.5L Pancreas 1.5L Small bowel 2.0L
What is the reserve capacity of the colon?
The colon can absorb up to 6 litres if needed (i.e. if a person has diarrhoea which comes from the small intestine)
Does diarrhoea come from the small or large intestine?
Both
What is the primary cause of diarrhoea in developed and developing countries?
Developed - viral
Developing - bacterial
What is Gastroenteritis?
Gastroenteritis - inflammation of the intestines and the stomach
What is the most common cause of ‘gastro’
Non specific
- no defined cause could be virus bacteria or protozoa (never fully investigated)
What is the causative agent of dysentery?
Shigella/EIEC, protozoa (Entamoeba histolytica)
What are the main foodborne causes of diarrhoea?
Salmonella, Vibrio, Listeria, Yerisinia, Cmpylobacter, EHEC viruses, Clostridium, Bacillus, Ciguatoxin etc
What is the most common cause of food borne diarrhoea in Aus?
Salmonella
What happens when clostridum perfinges is ingested?
It is normally found in spore form, when it enters the gut it sporylates and can release its toxin
where is Ciguatoxin found?
It is found in fish and can be very dangerous (it can kill)
What is travellers diarrhoea?
People become immune to infectious agents to the immediate area - if you go to visit places later in life are not immune to pathogens in the water/area
What are some causes of travellers diarrhoea?
ETEC, other bacteria, viruses, protozoa
What is colitis?
Inflammation of the colon
What is the causative agent of pseudomembranous colitis?
Clostridium difficile
The colitis is thought to occur when this bacterium replaces normal gut flora that has been compromised, usually following antibiotic treatment for an unrelated infection. The disturbance of normal healthy bacteria may provide C. difficile an opportunity to overrun the intestinal microbiome. It is a type of antibiotic-associated diarrhea.
When does pseudomembranous colitis occur?
thought to occur when this bacterium replaces normal gut flora that has been compromised, usually following antibiotic treatment for an unrelated infection. The disturbance of normal healthy bacteria may provide C. difficile an opportunity to overrun the intestinal microbiome
What are the causative agents of cholera-like diarrhoea?
Vibreo cholerae (If an epidemic of Cholera is suspected, the most common causative agent is V. cholerae O1. If V. cholerae serogroup O1 is not isolated, the laboratory should test for V. cholerae O139) ETEC
What is enteric fever?
Typhoid fever is a type of enteric fever along with paratyphoid fever.
What are the classic symptoms of non-specific gastro?
Loose stool. Not watery
What are the classic symptoms of dysentery?
Blood, pus and mucous in stool (Associated with invasive bacteria)
What are the classic symptoms of cholera-like diarrhoea?
Very watery gastro
What are the classic symptoms of enteric fever?
is a type of septicaemia, those infected are sick with a host of symptoms for a number of weeks.
What are the 5 pathotypes of diarrhoeagenic E. Coli
Enterotoxigenic E. coli (ETEC) Enteropathogenic E. coli (EPEC) Enterohemorrhagic E. coli (EHEC) Enteroinvasic E. coli (EIEC) Enteroaggregative E. coli (EAEC)
What are the symptoms of ETEC?
Watery diarrhoea
What are the symptoms of EPEC?
Non-specific gastro
What are the symptoms of EIEC?
Dysentry
What are the symptoms of EHEC?
Bloody diarrhoea
What are the symptoms of EAEC?
Watery diarrhoea
Who is most at risk of contracting ETEC?
Infants in LDs; travellers
Who is most at risk of contracting EPEC?
Children in LDCs
Who is most at risk of contracting EIEC?
Any age, mainly in LDCs
Who is most at risk of contracting EHEC?
Any age developed countries
Who is most at risk of contracting EAEC?
Children in LDCs
What are the adhesins and toxins of ETEC?
A = CFAs T = Enterotoxins
What are the adhesins and toxins of EPEC?
A = Intimin, Bfp T = T3S effectors
What are the adhesins and toxins of EHEC?
A = Intimin, Efa T = Shiga toxins
What are the adhesins and toxins of EIEC?
A =IpaC etc.
T = ShET
What are the adhesins and toxins of EAEC?
A = AAF T = Pet, EAST
What is the MOA of ETEC?
Heat Labile Enterotixin of ETEC = same action as cholera toxin
1) Toxin binds via B on membrane.
2) Retrograde vesicular transport through Golgi/ER -> release of A1 subunit ->
3) activation of Adenyl CycalseC increase in cAMP ->
4) activates CFTR (Cl- channel)
5) Cl- efflux from cells in SI and NaCl influx blockade in villus ->
6) accumulation of electrolytes in lumen as CL and Na are in the lumen.
7) -> diarrhoea.
Heat Stable:
1) Binds and activates GC -> accumulation of cGMP in gut.
2) Leads to Cl- efflux from si CELLS, and NaCl blockade at the villus electrolyte accumulation in intestinal lumen -> diarrhoea
Do ETEC invade the GIT?
Colonise but do not Invade.
MAO of EPEC
Stage 1:
• Initial adherence via Bundle forming Pili and attach to intact Microvilli. (plasmid encoded).
Stage 2:
• Lose Microvilli (effaced -> very intimate attachment of EPEC to the effaced enterocytes.
• This morphological change is ass with the original binding by the BFP activating a series of genes encoded on a pathogenicity island called LEE (encodes genes that enable tight binding).
MAO of EHEC
Shiga toxin (Stx): 1. B subunit binds to Gb3 2. -> retrograde transport via vesicle through Golgi/ER 3. -> A1 subunit activated and binds to 28S rRNA of 60S subunit 4. -> inhibits translation. • Gb3 found on endothelial cells: (i) lamina propria, (ii) glomerulus (renal problems), (iii) pancreas (diabetes), heart, (iv) Brain.
II
- EHEC ingested in food/water
- Attach to intestinal mucosa (e.g. using LEE PI).
- Produce Shiga toxin (cytotoxic)
- Toxins absorbed from gut intact binds Gb3 on En cells damage BVs supplying gut, kidney etc.
- HUS occurs when endothelial damage stimulates the coagulation cascade fibrin clots haemolysis of RBCs together with organ damage (kidney, pancreas, heart, brain).
- EHEC is most common cause of paediatric renal failure.
MOA of EIEC
- Only E. coli that INVADES enterocytes! Invades enterocytes of LI
- Spread to adjacent cells INFLAMMATION
- EIEC & Shigella only invade to mucosa. Salmonella typhi invades to blood.
- Induce damage, ulceration, inflammation dysentery.
- V similar to shigella. Shigella invades and may release shiga here which can get in and do what it did in EHEC
MAO of EAEC
- Characteristic pattern of adhesion to SI
- Cause of persistent diarrhoea
- EAEC lie down on enterocyte surface and stack themselves up like bricks.
What does EHEC bind to?
Binds to endothelial cells not enterocytes
Name 2 adhesive enterotoxigenic diarrhoea causing bacteria:
cholera and ETEC
Name a bacteria which adheres to the brush border and causes damage
EPEC
Name a bacteria that restricts its invasion to the mucosa?
Shigella
Name 2 bacteria which invade the submucosa:
Salmonella and Campylobacter
Which bacteria invades systematically?
Salmonella
Why doesn’t EIEC need such a well defined colonisation system?
They colonise the large intestine where food moves slower, thus it does not need high powered grappling hooks to hang on.
what are the 4 virulence factors?
Adehesins
Exotoxins
Invasive ability
Ability to resist killing